cash flow vs net operating income, needs some help

[Victor Rao]

I am new investor, interested in a 4 unit property in Manchester ct area, I need some help understanding if I am looking at a good investment or not? Please let me know , am I under or over estimating costs / returns?

I ran some numbers

asking price 320 k 

here are my assumptions 5% interest rate,  25%down payment, property tax 8k, insurance 6k, maintenance 7k, other costs 2k, monthly rent 4 k

I used the calculator.net rental calculator, I got first year cash flow 3.5k k , NOI number comes up as 22k . IRR=5.8%

I did not include management costs looks like a not a good investment, to me. 

what should be the average IRR for real estate investments.

what should be cash flow is there a bench mark number you guys look for?